Metal is one of the most commonly found contaminants in food and can be introduced at all stages of food manufacturing. By identifying metal contaminants during processing or packaging, a metal detector ensures the safety and the integrity of a wide range of goods and eliminates metal contaminants from a food manufacturer’s finished product.
How metal detectors work
There are several types of metal detectors, and each uses a different detection method to operate. In the food industry, metal detectors usually apply the balanced coil method. These metal detectors are equipped with a transmitter coil, which generates an electromagnetic field, and two receiver coils. The receiver coils have an equal but opposite output, creating a balanced state.
When a conductive object passes through the detector, it interrupts the balanced state of the electromagnetic field and causes a signal that is detected by the receiver coils. The electronic unit in the metal detector then analyses this signal, evaluates it, signals a metal detection, and either activates the automatic reject units that separates the contaminated product from the production line or alerts the operators.
Metal detectors are strategically placed based on areas where foreign materials can enter the production stream. If consumer protection is the goal, several inspection points are useful. Inspection of raw material catches metal particles before they are broken into smaller pieces which tend to be harder to detect. If the metal detector is used for machinery protection, it is installed directly before the machine requiring protection.
Inspections at critical control points (ie hazard analysis critical control points) during the production process are recommended so operators are alerted of machinery failures (eg broken blades, missing hardware) in a timely manner.
Consequently, after packaging, food products often are inspected at their final stage with a metal detector (and/or an X-ray system) to fully exclude contamination before being sent to the retailers’ shelves.
For optimal product protection, an inspection of raw materials at several critical control points and a final inspection of the finished product are recommended.
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